Water heater for removing particulates and returning water without particulates to heater, and method of operating same

ABSTRACT

A water heater for heating water containing particulates comprises a recirculating path responsive to water and particulates in the heater. The recirculating path removes particulates from the water flowing therein and returns water with particulates removed from it to the heater. The path includes a particulate filter for removing particulates from the water flowing in the path and a pump for pumping water in the path back into the heater. The path is responsive to a liquid cleaning agent applied to the heater with the water returned to the heater.

RELATION TO PREVIOUSLY FILED APPLICATION

[0001] The present application includes subject matter disclosed in theco-pending application of Frasure et al., Ser. No. 09/929,495, filedAug. 15, 2001.

FIELD OF INVENTION

[0002] The present invention relates generally to water heaters havingprovisions for minimizing the effects of particulate material in theheater and to a method of operating same and, more particularly, to sucha water heater and operating method wherein particulate material isremoved from the water and the water from which the particulate materialhas been removed flows back to the tank.

BACKGROUND ART

[0003] Particulate material enters water heaters with cold water or isproduced in the heater in response to elevated water temperatures thatproduce carbonates. In household water heaters, the particulate materialforms sediment that settles to the bottom of a tank where theparticulates accumulate. Frequently, the sediment accumulates inhousehold water heater tanks to such an extent that an electric waterheater coil becomes completely covered, reducing heat exchangeefficiency materially, and possibly causing the coil to becomeoverheated to such an extent that the coil breaks. In gas water heaters,the sediment accumulates between a burner and the water to reduce theheat transfer efficiency. In electric and gas water heater tanks, thesediment coats the interior walls of the tank, adversely affectingheater efficiency. Particulates also have an adverse effect on so-calledinstantaneous water heaters, which are frequently used for industrialpurposes; an example of such an instantaneous hot water heater isavailable from Rinnai Kabushiki Kaisha, Nagoya, Japan. In aninstantaneous water heater, cold water flows into a heater exchangerheated by gas flames.

[0004] In some water heaters, the particulates are accumulated assediment that is evacuated from the water heater through the wateroutlet, by being discharged through a water faucet or trapped in thefaucet strainers. The sediment trapped in the strainers should beeventually cleaned by unscrewing the strainer.

[0005] Other water heaters, e.g., Sigler, U.S. Pat. No. 4,505,231, andTaylor, U.S. Pat. No. 3,762,395, have manually operated sediment drainvalves to drain the particulates in the form of accumulated sedimentfrom the bottom of the water heater. The previously mentioned co-pendingapplication discloses an arrangement wherein particulates areaccumulated as sediment at the bottom of a tank and are automaticallyremoved through a valve from time to time. A problem with these waterheaters wherein particulates are removed from the tank is that asubstantial amount of water is usually drained from the tank with theparticulates.

[0006] It is, accordingly, an object of the present invention to providea new and improved method of and apparatus for minimizing adverseeffects of particulates in a water heater.

[0007] Another object of the invention is to provide a new and improvedmethod of and apparatus for operating a water heater whereinparticulates are removed from the water heater without removing asubstantial amount of water from the heater.

SUMMARY OF THE INVENTION

[0008] In accordance with one aspect of the invention, a gas or electricwater heater particularly adapted to heat water containing particulatescomprises a recirculating path arranged to be responsive to water andparticulates in the heater. The recirculating path is arranged to removeparticulates from the water flowing therein and to return water withparticulates removed from it to the heater.

[0009] Another aspect of the invention relates to a method of operatinga water heater. The method comprises supplying water includingparticulates to the water heater. The water in the water heater isheated. Some water and particulates from the water heater are removedfrom time to time and some particulates from the water are removed fromthe water heater from time to time. The water removed from the waterheater is returned to the water heater from time to time.

[0010] In a preferred embodiment, the recirculating path includes aparticulate filter for removing particulates from the water flowing inthe path. The recirculating path is preferably arranged to be responsiveto a liquid cleaning agent for dislodging particulates from surfaces inthe water heater. The recirculating path preferably includes a pump forpumping water and/or the cleaning agent in the path back into theheater. The pump is preferably downstream of the filter.

[0011] The above and still further objects, features and advantages ofthe present invention will become apparent upon consideration of thefollowing detailed descriptions of several specific embodiments thereof,especially when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING

[0012]FIG. 1 is a front elevation view of a household electric waterheater in accordance with a preferred embodiment of the invention;

[0013]FIG. 2 is a top sectional view of FIG. 1 taken along lines 2-2;

[0014]FIG. 3 is a bottom sectional view of FIG. 1, taken along lines3-3;

[0015]FIG. 4 is a side view of a manifold included in the heater ofFIGS. 1-3;

[0016]FIG. 5 is a front elevation and section view of a householdgas-fired water heater in accordance with a preferred embodiment of theinvention; and

[0017]FIG. 6 is a top section view taken along lines 6-6 of FIG. 5.

DETAILED DESCRIPTION OF THE DRAWING

[0018] The household electric water heater of FIGS. 1-4 includes closedtank 10 having an upper section containing outer vertically extendingcylindrical wall 15 and a lower section having a conical wall 20 thathas a downward constant slope, i.e., inclination, angle α of at least 42degrees from the horizontal. The bottom of conical wall 20, at centraldrain 21, is connected to pipe 24, thence to enlarged elbow 25, which isconnected to manual ball valve 30, in turn connected to automaticsolenoid operated drain valve 35 which is connected to pipe 36. Thus,the electric water heater of FIGS. 1-4 includes: bottom portion conicalwall 20 intersecting outer vertical wall 15, and electric heater coils45. The conical wall slopes downwardly from its intersection 26 withouter vertical wall 15 toward a central vertical axis of tank 10 wheredrain 21 is located. Drain valve 35 is actuated by timer controller 40which can be adjusted for the length of valve opening and the time ofday. Typically, valve 35 is opened daily, e.g. in the middle of thenight, for a period sufficient to cause about a half gallon of water toflow from tank 10 to pipe 36.

[0019] Water and particulates in pipe 36 flow into an inlet ofparticulate filter 37 having an outlet connected to an inlet arm of Tjoint 38. T joint 38 has a leg connected to source 39 of a leg connectedto source 39 of liquid cleaning agent, e.g., vinegar or acetic acid,that removes particulates from surfaces in tank 10 by a chemicalreaction. Source 39 is connected to joint 38 via solenoid valve 41 thatis opened by timer controller 40 simultaneously with opening of valve35. T joint 38 has an outlet arm connected to an inlet of pump 42 thattimer controller 40 turns on at the same time it opens valves 35 and 41.Pump 42, when turned on by controller 40, sucks (1) water that flowsthrough filter 37 and which has had particulates removed from it by thefilter and (2) cleaning liquid from source 39. The liquid cleaning agentchemically reacts with and dislodges impurities on surfaces in the waterheater to clean these surfaces and provide a flow of particulates tofilter 37. The dislodged particulates are trapped by filter 37 so thewater at the outlet of pump 42 has no substantial particulates therein.The liquid at the outlet of pump 42 flows via pipe 44 and T joint 43back into tank 10 to form a recirculation path as described in moredetail infra.

[0020] The water temperature is set by electric heaters 45 andadjustable temperature controller 50. Heaters 45 are in heat exchangerelation with the water inside tank 10. For clarity, the drawing doesnot include heater insulation which covers all sections of the heaterand hot water pipe 60. Penetrating heater roof 65 are pressure andtemperature relief valves 70, vertically extending cold water inlet pipe75 (frequently referred to as a dip tube) and corrosion reducing anode80. T joint 43 is inserted in pipe 75, about half between roof 65 andthe bottom end of pipe 75.

[0021] The opposite arms of T joint 43 are connected to the centerportion of pipe 75, while the leg of T joint 43 is connected to theoutlet of pump 42 via pipe 44. Thereby water that is relatively free ofparticulates and is clean flows from pump 42 to the lower portion oftube 75 via T joint 43. While the outlet of pump 42 is preferablyapplied to a center portion of pipe 75 to reduce the load on the pumpand somewhat isolate the pump output from the head of the water appliedto the inlet of pipe 75 and slits in the tube 92, it is to be understoodthat the outlet of pump 42 can be connected to any appropriate point intank 10.

[0022] Hand hole cover 85 provides access to the tank interior formanual cleaning and inspection.

[0023] As illustrated in FIGS. 1 and 2, the bottom end of dip tube 75,just above horizontal intersection 26 between cylindrical wall 15 andconical wall 20, is connected to T joint 90, having horizontallydisposed opposite ends connected to opposite ends of metal tube 92. Tube92 is shaped as a ring, held in place by hangers 89 (not shown in FIG. 1to simplify the drawing) so the tube outer surface is about an inch fromthe interior surface of wall 15, to hold tube 92 so that the tube ismounted essentially horizontally about an inch above intersection 26.

[0024] Tube 92 is a generally horizontally extending manifold includinga plurality of openings dimensioned and arranged so the water enteringtube 92 from tube 75 flows gently from tube 92 through the openingstherein without causing turbulence in the water in the remainder of tank10. The openings do not have a nozzle effect and have an area such thatthe flow rate of water passing through them does not cause turbulence tothe water or sediment in tank 10. The openings are only in a bottomportion of tube 92, such that water flowing through the opening does notflow upwardly in tank 10.

[0025] To these ends, tube 92 includes three sets 96, 97 and 98 ofslits. In an actual water heater, tube 92 included a total of 48 slits.

[0026] In essence, tube 92 includes first and second segments 93 and 94,respectively connected to the opposite ends of T joint 90 so that thewater in the bottom of dip tube 75 flows from the dip tube into segments93 and 94 in opposite directions from the T joint, which thus forms acommon point for the water to flow in opposite directions.

[0027] The angled slits in set 96 are in segments 93 and the angledslits in set 97 are in segment 94. The slits in sets 96 and 99 in bothsegments 93 and 94 are angled in the same direction as the laminar flowof water in these segments. The slits in set 98 that are in segments 93and 94 are substantially perpendicular to the direction of laminar flowof water in tube 92. In the actually constructed water heater, there wasa total of 48 slits; 22 slits in set 96, 22 slits in set 97, and fourinterspersed right angle slits in set 98. Each slit had a width of about{fraction (1/16)} inch and a length of about 1 ½ inches. The slits ofsets 96 and 97 are tilted about 20 degrees relative to the direction oflaminar water flow in tube 92.

[0028] In response to water being removed from tank 10 through hot waterpipe 60 while valves 35 and 41 are closed and pump 42 is off or throughpipe 36 while valves 35 and 41 are open and pump 42 is on, water flowsfrom the bottom of dip tube 75 into tube 92, thence through the slits insets 96-98 into the bottom portion of tank 10. Water flows through theslits in sets 96-98 in response to water flowing out of hot water pipe60 or opening of drain valve 35. In the former case, water enters thetop of cold water pipe 75 as shown at arrow 110. In the latter case,water enters pipe 75 from pump 42 through T joint 43. In both cases,water in the bottom of pipe 75 flows through the slits in sets 96-98.The water flowing through the slits in sets 96-98 gently washes sedimentin the bottom portion of the tank toward conical horizontally andvertically extending wall 20. The inclination angle, α, of wall 20 belowthe horizontal plane is such that the washed sediment 95 accumulates atand in proximity to drain 21.

[0029] Controller 40 automatically and simultaneously (1) opens valves35 and 41 and (2) activates pump 42 from time to time, e.g.,periodically, to remove the washed sediment 95 (FIG. 2) from the bottomportion of tank 10 via drain 21 to prevent accumulation of substantialsediment in the tank. Because the washed sediment lodges in the filter37, which is outside of the heat exchange region of tank 10, the adverseeffects of sediment accumulation in tank 10 are avoided.

[0030] Timer and valve controller 40 activate solenoid valve 35 forvarying durations and frequencies depending on the hardness of the waterand amount of particulate residue in the water. The timer is typicallyset to actuate the solenoid valves 35 and 41, as well as pump 42, forabout 3 seconds during the middle of each night. Depending on waterpressure and component sizes, in this 3-second period about one cubicfoot of water flows in a recirculating path from valve 35 to T joint 43via filter 27 and pump 42. This one cubic foot of water drains only thecool water located in the lower portion of tank where conical wall 20 islocated. The hot water above lower heating coil 45 is not dischargedsince the lower coil 45 is about 4 inches above the top of inverted cone20.

[0031] The household gas fired heater illustrated in FIGS. 5 and 6includes tank 140 having cylindrical wall 145 and lower sectionincluding an inverted conical wall 150 having a minimum downward slopeangle, β, of at least 42 degrees from the horizontal for optimumoperation. Drain 152, at the bottom of inverted cone 150, is adjacent toelbow 155, connected to manual ball valve 160, in turn connected toautomatic solenoid operated drain valve 165. Drain valve 165 is actuatedby timer/controller 170 which is adjusted to control the valve openingduration and the time of day the valve is opened. Water flowing throughvalve 165 flows via pipe 166 to an inlet of particulate filter 167.Filter 167 has an outlet connected to an inlet arm of T joint 168,having a leg connected via solenoid valve 172 to source 169 of a liquidcleaning agent, e.g., acetic acid or vinegar. T joint 168 has an outletarm for supplying water that flows through filter 167 and has hadparticulates removed from it and liquid from source 169 to an inlet ofpump 171. Pump 171 has an outlet for supplying the water from filter 167and the liquid from source 169 back to tank 140, to form a recirculationpath for water removed from tank 140 via valve 165. Timer controller 170turns on pump 171 and opens valves 165 and 172 simultaneously,preferably during the middle of each night, a period when hot water isnot usually flowing through pipe 185.

[0032] The water heater temperature is set by (1) gas control valve 175,(2) annular gas jet manifold 176, which is located under cone 150 topreclude water contact with the flame, and (3) adjustable temperaturecontroller 180. For clarity, the drawing does not show heater insulationwhich covers all sections of the heater and hot water outlet pipe 185.Penetrating the heater top section 186 are pressure and temperaturerelief valves 190, cold water inlet pipe 195, and corrosion reducinganode 200. Flue pipe 201 penetrates the center of the top section 186and extends down to the top of inverted cone 150. Within flue pipe 201,is tubing coil 202 that, by convection, moves cool water in tank 140from inlet 203 of flue pipe 201, to an outlet (not shown) near the topcover 186. Handhold cover 205 provides access to the tank interior formanual cleaning and inspection. The water in tank 140 is in heatexchange relation with hot gas from manifold 176 by virtue of metal cone150 and metal flue pipe, being in contact with the water and heatedprimarily by convection by the hot gas.

[0033] Because gas jet manifold 176 is below cone 150 and flue pipe 201is located in the center of tank 140, drain 152 cannot be centrallylocated. Consequently, drain 152 is located in proximity to exteriorwall 145, at the lowest portion 220 of flange 240 that extends from thelowest edge of cone 150 and is bonded, e.g., by seam welding orsoldering, to wall 145. Cone 150 forms a vertically and horizontallyextending bottom wall portion of tank 140. The bottom edge of cone 150has a zenith point 222 diametrically opposite from drain 152, which isat the nadir of the cone bottom edge. In each vertical cross section oftank 140, flange 240 extends horizontally between the bottom edge ofcone 150 and wall 145. Flange 240 extends continuously and smoothlyaround the circumference of the bottom edge of cone 150, between zenithpoint 222 and drain 152 to, in effect, provide a runway for sedimentincident on the flange and cone 150. The inclination angle β of thehorizontally and vertically extending wall of cone 150 relative to thehorizontal plane is such that washed sediment in tank 140 drifts bygravity along the wall of cone 150 to the runway flange 240 forms.Inclination angle β continuously varies from a minimum angle along astraight line of the wall segment between flue 201 and zenith point 222to a maximum angle along a straight line of the wall segment betweenflue 201 and nadir 220. The inclination angle of the runway betweenzenith point 222 and drain 152 is such that the washed sediment incidenton the runway also drifts by gravity to the drain. The optimum minimuminclination angle β is 42 degrees below a horizontal plane extendingthrough a horizontal intersection of cone 150 and flue 201.

[0034] At the lowest end of dip tube 195 is horizontally extending Tjoint 210 for directing cold water horizontally in two directions intotube or manifold 212. Manifold 212 is connected to the bottom of coldwater inlet tube 195 and fixedly mounted by hangers (not shown) justabove zenith point 222. Manifold 212 is shown as being horizontallydisposed, but it is to be understood that the manifold could be inclinedso it is a fixed distance above flange 240. Manifold 212 includes manyslits 214 completely along its length. The slits 214 are only in thelower half of the metal tubing forming manifold 212. Manifold 212 issimilar to manifold 92 in that slits 214 are dimensioned and arranged sothe cold water flows gently through slits 214 without causing turbulenceto the sediment and/or water in tank 140. Slits 214 in manifold 212 canachieve this result by having the same dimensions as the slits ofmanifold 92. Slits 214 differ from the slits of manifold 92 because allof slits 214 are perpendicular to the direction of laminar water flow inthe annular tube forming manifold 212. One actually built manifold 212has 48 slits 214, spaced 1 inch from each other along the circumferenceof the manifold.

[0035] In response to water exiting hot water pipe 185, shown by arrow230, cold water enters cold water pipe 195 as shown at arrow 235. Inresponse to water and particulates flowing through drain valve 165, theparticulates are removed from the water by filter 167. The water flowingthrough filter 167 and the cleaning liquid flowing through open valve172 are sucked by pump 171 to flow via T joint 173 into a midpoint ofpipe 195 about half way between roof 186 and manifold 212. In bothcases, water flows to the bottom of pipe 195, thence to manifold 212 andthrough slits 214 to gently wash sediment in tank 140 to the wall ofcone 150, thence to the runway that flange 240 forms and to drain 152.

[0036] The gas water heater has convex roof 186 and vertical sides ofabout 40 inches. The bottom edge of cone 150 at zenith point 222 isabout 8 inches below the bottom of flue 210; at nadir 220, the conebottom edge is about 12 inches below the bottom of flue 210. A 1.5 inchdiameter outlet and a 90 degree elbow 155 are connected adjacent todrain 152, at nadir 220 of cone 150. A bell reducer reduces the pipingfrom 1.5 inch diameter to 1.25 inch diameter. Stainless steel ball valve160 isolates stainless solenoid valve 165 for maintenance orreplacement. Tank 140 is about 2 feet in diameter and has a volume ofabout 33 gallons. Stainless steel inlet dip tube 195 terminates at the90 degree T joint 210 about one inch above the bottom edge of cone 150.Three legs support the tank and can therefore accommodate uneven floors.The preferred tank material is stainless steel surrounded by foaminsulation and a think outer metal shell.

[0037] The electrical components include pump 171, as well as solenoidvalves 165 and 172, and timer and valve controller 170. Timer and valvecontroller 170 is adjusted to activate pump 171 as well as solenoidvalves 165 and 172 for varying durations and frequencies depending onthe hardness of the water and amount of particulate residue in thewater.

[0038] Although the materials referred to for construction are stainlesssteel, a less expensive heater could be made from a glass-lined carbonsteel body using copper pipe and bronze valves.

[0039] While the present invention has been described by reference tospecific embodiments, it will be apparent that other alternativeembodiments and methods of implementation or modification may beemployed without departing from the true spirit and scope of theinvention. For example, the recirculating path for removing particulatescan be employed to remove particulates that lodge in heat exchangers ofso-called instantaneous industrial hot water heaters, of the typepreviously discussed in the Background Art portion of this document. Insuch a case, a first T joint is connected in the cold water pipe leadingto the heat exchanger. A second T joint is connected in a by-pass pipeconnected, via a by-pass valve, between the heat exchanger hot wateroutlet pipe and the cold water inlet of the heater. A particulate filterhas an inlet connected to a leg of the second T joint and an outletconnected via a third T joint to an inlet of a pump having an outletconnected to a leg of the first T joint. The third T joint is alsoresponsive to cleaning liquid that flows through a suitable solenoidvalve that is opened simultaneously with activation of the pump, at atime when hot water is not removed from the heat exchanger. It is alsoto be understood that in some circumstances the cleaning liquid sourceand plumbing associated therewith are not necessary. The particulatefilters are typically of a type wherein a filter element is easilyremoved. Further, backwash techniques can be employed for removingparticulates from the particulate filter from time to time, at intervalsmuch less frequent than activation of the recirculation path. In apractical household water heater, the recirculation path is typicallyintegral with the tank, and the filter and cleaning agent are located sothey can be easily accessed.

We claim:
 1. A water heater particularly adapted to heat watercontaining particulates, comprising a recirculating path arranged to beresponsive to water and particulates in the heater, the recirculatingpath being arranged to remove particulates from the water flowingtherein and to return water with particulates removed from it to theheater.
 2. The water heater of claim 1 wherein the recirculating pathincludes a particulate filter for removing particulates from the waterflowing in the path.
 3. The water heater of claim 2 wherein therecirculating path includes a pump for pumping water in the path backinto the heater.
 4. The water heater of claim 3 wherein the pump isdownstream of the filter.
 5. The water heater of claim 4 wherein therecirculating path is arranged to be responsive to a liquid cleaningagent and the pump is arranged to pump the agent to the heater.
 6. Thewater heater of claim 5 wherein the recirculating path is arranged sothe liquid cleaning agent is introduced into the recirculating pathbetween an outlet of the filter and an inlet of the pump.
 7. The waterheater of claim 3 wherein the recirculating path is arranged to beresponsive to a liquid cleaning agent and the pump is arranged to pumpthe agent to the heater.
 8. The water heater of claim 1 wherein therecirculating path is arranged to (a) be responsive to a liquid cleaningagent and (b) supply the cleaning agent to the heater.
 9. The waterheater of claim 8 wherein the recirculating path includes a pump forpumping water and the liquid cleaning agent in the path back into theheater.
 10. The water heater of claim 1 wherein the water heaterincludes a closed tank having a vertical exterior wall arrangement and abottom portion with a wall extending horizontally and vertically to anormally closed bottom drain, a valve arrangement coupled to the bottomdrain for selectively enabling water flowing through the bottom drain toflow through it to the recirculating path, a hot water outlet connectedto the tank interior, a cold water inlet having a segment in proximityto the horizontally and vertically extending wall, the cold water inletbeing arranged so that in response to water being removed from the tank,cold water flows from the inlet into the bottom portion to gently washsediment in the bottom portion toward the horizontally and verticallyextending wall, the horizontally and vertically extending wall beingarranged so the washed sediment drifts by gravity to the drain and thedrifted sediment accumulates at and in proximity to the drain, and acontroller for opening the valve from time to time for removing thewashed sediment from the bottom portion via the drain and preventingaccumulation of substantial sediment in the tank.
 11. The water heaterof claim 10 wherein the recirculating path is arranged for causing waterflowing through it to flow into the cold water inlet.
 12. The waterheater of claim 1 wherein the cold water inlet segment comprises agenerally horizontally extending manifold.
 13. The water heater of claim12 wherein the manifold includes a plurality of openings dimensioned andarranged so the cold water flows gently through them without causingturbulence in the water in the remainder of the tank.
 14. The waterheater of claim 13 wherein the manifold comprises a tube, the openingsbeing only in a portion of the tube such that water flowing through theopenings does not flow upwardly.
 15. The water heater of claim 14wherein the openings do not have a nozzle effect and have an area suchthat the flow rate of water passing through them does not cause water orsediment turbulence.
 16. The water heater of claim 11 wherein the waterheater includes an electric heating coil, the bottom portion wallintersecting the outer vertical wall arrangement and sloping downwardlyfrom its intersection with the outer vertical wall toward a central axisof the tank where the drain is located.
 17. The water heater of claim 11wherein the water heater includes a gas burner and a central flue influid flow relation with combustion products of the gas burner, the gasburner being below the bottom portion wall, the bottom portion wallhaving an intersection with the flue and sloping downwardly from itsintersection with the flue toward the outer vertical wall arrangement,the bottom portion wall having a sloping bottom edge having a nadir atthe drain and a runway between the sloping bottom edge and the outervertical wall arrangement; the cold water inlet segment, the bottomportion wall, the runway and the drain being arranged so that the washedsediment drifts to the bottom portion wall, thence drifts by gravity tothe runway, thence drifts by gravity to the drain.
 18. The water heaterof claim 1 wherein the water heater includes a gas burner.
 19. A methodof operating a water heater comprising supplying water includingparticulates to the water heater, heating the water in the water heater,removing some water and particulates from the water heater from time totime, from time to time removing particulates from the water removedfrom the water heater, and from time to time returning to the waterheater the water removed from the water heater.
 20. The method of claim19 wherein the particulates are removed from time to time from the waterremoved from the water heater by a filter.
 21. The method of claim 20wherein the water is returned to the water heater by pumping.
 22. Themethod of claim 21 further including supplying a liquid cleaning agentto the water returned to the water heater by pumping.
 23. The method ofclaim 22 wherein the liquid cleaning agent and the water returned to thewater heater by pumping are simultaneously supplied to the water heater.24. The method of claim 20 further including supplying a liquid cleaningagent to the water returned to the water heater.
 25. The method of claim24 wherein the liquid cleaning agent and the water returned to the waterheater are simultaneously supplied to the water heater.
 26. The methodof claim 19 wherein the surfaces in the water heater are cleaned bysupplying a liquid cleaning agent to the water returned to the waterheater.